1. Field of the Invention
The present invention relates to an optical disk reproducing unit and more particularly, to a unit for processing signals from a optical pickup.
2. Description of the Related Art
FIG. 1 depicts light receiving parts of a conventional optical pickup. The optical pickup has light receiving parts A, B, C, D, E and F. Each of them produces an output signal upon receipt of light. The output signals are amplified through corresponding amplifiers AMP to be produced as a, b, c, d, e and f. The focus exactness is detected with a gain difference between the addition of signals a and c and that of signals b and d in the above a, b, c and d. In addition, a degree by which the optical pickup is deviated from a track is detected by using a gain difference of the above signals e and f. A servo controls the optical pickup in accordance with the focus exactness and the information of optical pickup deviation. Errors of more than 10% may be made in output signals a, b, c, d, e and f from light receiving parts A, B, C, D, E and F by the mismatch with respect to those light receiving parts that may occur in the process of manufacturing the optical pickup. That is, during the manufacturing of the optical pickup, its light receiving parts A, B, C, D, E and F may be mismatched. The above errors serve as an offset of the server for controlling the optical pickup, which becomes problematic in a high-speed and high-precision optical disk player.
Referring to FIG. 2, depicting a circuit sensing the optical pickup deviation degree by the use of signals e and f (hereinafter, a tracking error sensing unit), signal e is input to an inverting input terminal of a differential amplifier A1 through a resistor R1. Signal f is input to a non-inverting terminal of differential amplifier A1 through a resistor R3. Differential amplifier A1 's output terminal is connected to its inverting input terminal through a resistor R2. The tracking error sensing unit produces a difference of signals e and f, and the transfer characteristics are expressed by equation 1: ##EQU1##
The above signal Vout is indicative of a difference of signals e and f and is input to a control device controlling the optical pickup. The control device controls to make the optical pickup keep the track with signal Vout.
If there is an error by the mismatch that may occur in the optical pickup manufacturing process, the conventional tracking error sensing unit does not exactly detect a tracking error with signals e and f.
As described above, there may be a mismatch with respect to light receiving parts A, B, C, D, E and F in the manufacture of the optical pickup, and errors of more than 10% may be made in its output signal by the mismatch. The errors serve as an offset of the servo for controlling the optical pickup, which becomes problematic in a high-speed and high-precision optical disk player.